15 amp fuse burns up when inserted (controls brake safety switch)

1996 econoline van 15 amp fuse continues to blow. Fuse is for brake switch. Without fuse cannot switch gears. Fuse controls brake lights, changing of gears or brake safety start switch, mph gauge. Please advise what this might be . I actually saw the fuse ignite and burn and was worried of an electrical fire.

There is a hot wire grounding out someplace. You haven't replaced any tail light bulbs? If one is in the wrong way it will blow the fuse. If they are all right I would be looking at the brake light switch at the pedal. Disconnect the wiring connector to it and see if the fuse still blows. It could be hard to find the problem because there are so many wires and connectors on the circuit. Don't worry about a fire, that's what the fuse is for. Just don't put in a bigger fuse.